http://www.mmo-champion.com/threads/915334-Reasons-not-to-buying-Blizzard-games-anymore
http://wow.joystiq.com/tag/Broken-Promises/
Main Points:
-They did not deliver on many core promises of World of Warcraft. (I can list more from experience)
-The quality of content is dropping to appease less intelligent people.
-One of the highlights of Blizzard games in the past pre-WoW was always story, I find the wait of D3's story to be lackluster at best.
-It's not hard to find broken Blizzard promises with 10 minutes of Google.